Insulative compositions, article incorporating the same and methods of forming the same

ABSTRACT

Precursors, insulative compositions, an article including the insulative compositions and a method for making the insulative compositions are disclosed. The insulative compositions are formed from a precursor composition that includes a nitride butadiene rubber, a nanoclay and a cure package including a sulfur-based curing agent. The insulative compositions may have a substantially reduced weight and compressive modulus in comparison to conventional insulative rubbers. Thus, the insulative compositions may provide improved ballistic properties in addition to reduced density and thickness. Precursor compositions for forming the insulative composition may have good flow characteristics. The insulative compositions may be used in a variety of applications, such as personnel body armor, ground vehicle armor and aircraft armor systems.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to co-pending U.S. patent applicationSer. No. 11/431,387 entitled BASALT FIBER AND NANOCLAY COMPOSITIONS,ARTICLES INCORPORATING THE SAME, AND METHODS OF INSULATING A ROCKETMOTOR WITH THE SAME, filed on May 9, 2009 and U.S. patent applicationSer. No. 12/765,585 entitled BASALT FIBER AND NANOCLAY COMPOSITIONS,ARTICLES INCORPORATING THE SAME, AND METHODS OF INSULATING A ROCKETMOTOR WITH THE SAME, filed on Apr. 22, 2010, each of which is assignedto the Assignee of the present application, and to co-pending U.S.patent application Ser. No. ______ (attorney docket no. 8421-91699),entitled MULTILAYER BACKING MATERIALS FOR COMPOSITE ARMOR, filed on evendate herewith and assigned to the Assignee of the present application,the disclosure of which is incorporated by reference herein in itsentirety.

TECHNICAL FIELD

The present invention relates to an insulative composition, articlesincorporating the insulative composition and a method of forming thesame. More specifically, embodiments of the present invention relate toan insulative composition including nitrile butadiene rubber and ananoclay and having physical, mechanical and rheological propertiessuitable for use in military applications, such as in personnel armor,ground vehicle armor and aircraft armor systems.

BACKGROUND

Particulate fillers, such as silica, have conventionally been used asreinforcing materials for polymer materials, such as nitrile butadienerubber (NBR), to improve physical properties such as compressivemodulus, tensile strength, abrasion, tear properties and dynamicproperties. For example, a silica-filled nitrile butadiene rubber(SFNBR) has been used for ballistic applications.

Because silica has strong filler-filler interactions and adsorbs polarmaterials, silica-filled rubber compounds exhibit poor dispersion of thefiller and poor cure characteristics. Furthermore, conventional SFNBRoften may include fibers and are, thus, anisotropic materials havingdifferent properties when measured along different directions therein.Currently available SFNBR compositions also have undesirably highspecific gravities and compressive modulus. The conventional SFNBRcompositions include high contents of NBR which result in highviscosities (i.e., Mooney viscosities of greater than about 50) and flowissues. Silica has also been shown to significantly retard the cure rateof the SFNBR, which may be attributed to the adsorption of curatives onthe silica surface. Furthermore, conventional SFNBR compositions includecomponents that are either difficult to obtain or are not available inthe United States.

Recently, there has been considerable interest in forming polymermaterials reinforced with nanosized particles, often referred to as“nanocomposites.” Such nanocomposites conventionally include nanoclayparticles dispersed in a polymer material. Smectite clays, such asmontmorillonite clays, are most commonly used as nanoclays innanocomposites due to their high cation exchange capacities, largesurface area, good surface reactivity and surface adsorptive properties.Depending on an amount of dispersion of the nanoclay particles withinthe polymer material, the nanocomposite may have either an intercalatedstructure or an exfoliated structure. In an intercalated nanocomposite,layers of the polymer material are disposed between sheets of thenanoclay particles. In an exfoliated nanocomposite, the polymer materialis completely dispersed within the sheets of nanoclay particles.

Development of nanocomposites is difficult, however, becausethermodynamic and kinetic barriers inhibit dispersion of the nanoclayparticles in the polymer material. For example, the hydrophilic natureof nanoclay particles prevents dispersion and results in formation ofaggregates in the polymer material. Furthermore, mixing the nanoclayparticles with the polymer material may result in an uncured compositionhaving an undesirably high viscosity and inadequate flow properties foruse in certain applications.

Insulative compositions having improved processability and improvedproperties, as well as methods for making such compositions are desired.

BRIEF SUMMARY OF THE INVENTION

The present invention, in several embodiments, relates to an insulativecomposition that, before curing, includes at least one nitrile butadienerubber, a nanoclay and a sulfur-based cure package. For example, thenitrile butadiene rubber may be present in the insulative composition inan amount of between about 60% by weight and about 70% by weight and,more particularly, about 65.25% by weight of a total weight of theinsulative composition. The nanoclay may include a montmorillonite clay,such as CLOISITE® nanoclay. The cure package may include a sulfur-basedcuring agent. In addition to the sulfur-based curing agent, the curepackage may include at least one of tetramethyl thiuram disulfide andbenzothiazyl disulfide. As a non-limiting example, the insulativecomposition may include about 1.31% by weight of the sulfur-based curingagent, about 0.33% by weight of the tetramethyl thiuram disulfide, andabout 0.65% by weight of the benzothiazyl disulfide. The insulativecomposition may further include at least one of an amine antioxidant, aphenolic resin, stearic acid, dioctyl phthalate, and zinc oxide.

The present invention also relates to a precursor of an insulativecomposition that includes a polymer comprising at least one nitrilebutadiene rubber, a nanoclay and a cure package including a sulfur-basedcuring agent, wherein the precursor composition has a flowableconsistency. For example, the precursor composition may have a Mooneyviscosity of between about 5 and about 30 and, more particularly about24.4.

The present invention also relates to an article of manufacture thatincludes a sheet of fibrous material and insulative composition disposedon the sheet of the fibrous material and including at least one nitrilebutadiene rubber, a nanoclay and a cure package comprising asulfur-based curing agent and at least one of tetramethyl thiuramdisulfide and benzothiazyl disulfide.

The present invention also relates to a method of forming a precursor ofan insulative composition that includes exfoliating a nanoclay with apolymer comprising at least one nitrile butadiene rubber to form amaster batch comprising a substantially homogeneous mixture of thepolymer and the nanoclay, mixing a portion of the master batch with acure package comprising a sulfur-based cure agent to form a mixture andcombining a remaining portion of the master batch with the mixture toform a precursor having a flowable consistency. The polymer may be mixedwith the nanoclay for between about 5 minutes and about 25 minutes toexfoliate the nanoclay with the polymer forming the master batch. Anamine antioxidant and a phenolic resin may additionally be incorporatedinto the master batch. For example, about one-half of a total volume ofthe master batch may be mixed with the cure package to form the mixture.

BRIEF DESCRIPTION OF THE DRAWING

While the specification concludes with claims particularly pointing outand distinctly claiming that which is regarded as the present invention,advantages of this invention may be more readily ascertained from thefollowing detailed description when read in conjunction with theaccompanying drawing in which:

FIG. 1 illustrates an embodiment of an article including an insulativecomposition of the present disclosure.

DETAILED DESCRIPTION

Insulative compositions including a nitrile butadiene rubber (NBR) and ananoclay, such as CLOISITE® nanoclay are disclosed, and may beformulated to have a low specific gravity and compressive modulus. Asused herein, the term “nanoclay” means and includes a clay material inthe form of fine particles having an average primary dimension of lessthan about 100 nm. The insulative compositions may be used as insulationfor an armor material, or in association with another article orassembly that would benefit from protection from impact. The insulativecomposition may have improved rheological, physical and mechanicalproperties in comparison to a conventional SFNBR composition. Forinstance, a specific gravity and compressive modulus of the insulativecomposition of the present invention may be substantially lower than thespecific gravity and the compressive modulus of conventional SFNBRcompositions. The reduced compressive modulus of the insulativecomposition provides improved strength and shock absorption. The reducedspecific gravity of the insulative composition provides reduced weight.Accordingly, the insulative composition may provide similar or improvedballistic properties at densities and/or thicknesses of less than orequal to those of the conventional SFNBR compositions. The insulativecomposition of the present invention is fiber-free and, thus, is anisotropic material having substantially uniform properties throughout.Furthermore, the compounds used to form the insulative composition arereadily available.

A precursor composition of the insulative compositions is alsodisclosed. The precursor composition may exhibit a sufficiently lowviscosity such that the precursor composition has a flowableconsistency. As used herein, the terms “flowable” and “free-flowing”mean and include a sufficiently low viscosity that enables material tochange shape or direction substantially uniformly in response to anexternal force (e.g., gravity or a weight of the material itself) suchthat the material readily flows out of a container at room temperature.For example, a Mooney viscosity (Vm) of the precursor composition may beless than or equal to about 30 Mooney units at a temperature of betweenabout 20° C. to about 100° C. and, more particularly, may be betweenabout 15 Mooney units and about 25 Mooney units at a temperature ofbetween about 20° C. and about 100° C.

Also disclosed is a method for forming a precursor composition thatprovides increased exfoliation of the nanoclay within the NBR in thecured insulative composition. As used herein, “exfoliation” means andincludes a delamination process wherein individual sheets or plateletsof the nanoclay particles are spatially separated by a polymer material(i.e., NBR), causing expansion of the layered nanoclay structure. Theatomic configuration of a nanoclay includes alternating sheets of atomicunits. For example, the nanoclay may be an alumina silica nanoclay thatincludes silica (SiO₄) tetrahedral and alumina (AlO₆) octahedral unitsthat are organized into a plurality of sheets or platelets by oxygensharing between units. During exfoliation of the NBR by the nanoclay,the NBR may enter into sheets of nanoclay particles, resulting ininterlayer spacing of the NBR and the nanoclay particles. As the sheetsof the nanoclay continue to separate from one another, spacing betweeneach of the sheets of the nanoclay is increased such that the sheets ofthe nanoclay become substantially homogeneously dispersed in the NBR.

The method may include mixing the NBR and the nanoclay for an amount oftime sufficient to substantially homogeneously distribute the nanoclayin the NBR. In some embodiments, the NBR and the nanoclay may be mixedwith an antioxidant and a processing aid for about 12 minutes todisperse the nanoclay in the NBR forming a substantially homogeneousmixture. Additives may optionally be mixed with the substantiallyhomogeneous mixture of the nanoclay and NBR to form a master batch. Acure package may be added to and mixed with a portion of the masterbatch, such as about one-half (½) of a total volume of the master batch.The cure package may include, for example, a sulfur-based curing agentand at least one cure accelerator. The remaining portion of the masterbatch may then be added to form a precursor composition having afree-flowing consistency. Increased distribution of the nanoclay in theNBR matrix may result in improved physical, mechanical and rheologicalproperties in the insulative composition.

The nitrile butadiene rubber used in the precursor of the insulativecomposition may be a nitrile butadiene rubber having an acrylonitrilecontent of between about 26 wt % and about 35 wt %, such as from betweenabout 30 wt % and about 35 wt %. As used herein, the phrase“acrylonitrile content” means and includes a percentage of boundacrylonitrile present in the NBR. Combinations of NBRs, each having anacrylonitrile content within the above-mentioned range, may also beused. The NBR may be unhydrogenated or hydrogenated. The precursor ofthe insulative composition may include between about 50 wt % and about80 wt % of a total weight of the precursor of the insulative compositionand, more particularly, between about 60 wt % and about 70 wt % of thetotal weight of the precursor of the insulative composition of the NBR.Examples of NBRs that may be used in the insulative composition include,but are not limited to, those sold under the NIPOL® tradename, such asNIPOL® 1042, NIPOL® 1052, NIPOL® 1052-30, NIPOL® 1312, or combinationsthereof. The NIPOL® nitrile butadiene rubbers are copolymers ofacrylonitrile and butadiene and are commercially available from ZeonChemicals (Louisville, Ky.). NIPOL® 1042 has an acrylonitrile content ofbetween about 32 wt % and about 34 wt %, a Mooney viscosity at 100° C.of between about 75 and about 90, and a specific gravity of 0.98. NIPOL®1052 has an acrylonitrile content of between about 32 wt % and about 34wt %, a Mooney viscosity at 100° C. of between about 45 and about 60,and a specific gravity of about 0.98. NIPOL® 1052-30 is a lower Mooneyviscosity version of NIPOL® 1052 and has an acrylonitrile content ofbetween about 32 wt % to about 34 wt %, a Mooney viscosity at 100° C. ofbetween about 25 and about 40, and a specific gravity of about 0.98.NIPOL® 1312 is a liquid NBR and has an acrylonitrile content of betweenabout 27 wt % and about 30 wt %, a Brookfield viscosity at 50° C. ofbetween about 20,000 centipoise (“cps”) and about 30,000 cps, and aspecific gravity of about 0.96. NBRs that may be used in the insulativecomposition are available under other tradenames including, but notlimited to, the KRYNAC® polymers and PERBUNAN® polymers, which arecommercially available from Bayer AG (Leverkusen, Germany), andPARACRIL® polymers, which are commercially available from UniroyalChemical Company (Middlebury, Conn.).

The nanoclay used in the insulative composition may include, forexample, clay from the smectite family. The term “smectite,” as usedherein, means and includes a group of particulate clay materials, suchas montmorillonite, beidellite, nontronite and saponite. Smectites havea unique morphology, including at least one dimension in the nanometerrange. The precursor of the insulative composition may include betweenabout 6 wt % and about 15 wt % of the total weight of the precursor ofthe insulative composition of the nanoclay and, more particularly,between about 8 wt % and about 12 wt % of the total weight of theprecursor of the insulative composition of the nanoclay. The nanoclaymay include, for example, a montmorillonite clay, such as a CLOISITE®nanoclay, which is commercially available from Southern Clay Products,Inc. (Gonzales, Tex.). CLOISITE® nanoclays include nanoparticles havinganisotropic, plate-like, high aspect-ratio morphologies. CLOISITE®nanoclays include organically modified nanometer scale, layeredmagnesium aluminum silicate platelets. The magnesium aluminum silicateplatelets may have a thickness of about 1 nm and a width of betweenabout 70 nm and about 150 nm. The magnesium aluminum silica plateletsare surface modified to enable complete dispersion into and providemiscibility with the NBR. For example, CLOISITE® 10 A nanoclay includesmagnesium aluminum silicate platelets modified with a quaternaryammonium salt. Table 1 shows physical properties and mechanicalproperties of CLOISITE® 10 A nanoclay.

TABLE 1 Properties of CLOISITE ® 10A nanoclay Specific Gravity  1.90g/cc Bulk Density 0.1636 g/cc (loose) 0.2647 g/cc (packed) Loss OnIgnition 39% Particle Size 10% less than: 2 μm 50% less than: 6 μm 90%less than: 13 μm Hardness, Shore D 83 Tensile Strength, Ultimate   101MPa Elongation at Break  8% Modulus of Elasticity  4.657 GPa FlexuralModulus   3.78 GPa Izod Impact, Notched   0.27 J/cm

The cure package may contain a sulfur-based curing agent and a cureaccelerator. Examples of sulfur-based curing agents include, but are notlimited to, laccofine sulfur, which is commercially available from S.F.Sulfur Corporation (Freeport, Tex.), CRYSTEX® OT-20 (an oil-treatedpolymeric sulfur), which is available from Flexsys America LP (Akron,Ohio), AKROSPERSE® IS-70 (a 70% sulfur dispersion), which is availablefrom Akrochem Chemical Corp. (Akron, Ohio), other forms of elementalsulfur, and combinations thereof. The sulfur-based curing agent may beincluded in the precursor of the insulative composition in an amount ofbetween about 0.5 wt % and about 3 wt % of the total weight of theprecursor of the insulative composition and, more particularly, betweenabout 1 wt % and about 2 wt % of the total weight of the precursor ofthe insulative composition.

Examples of cure accelerators include sulfides, such as tetramethylthiuram disulfide (TMTD), benzothiazol disulfide, such as NAUGEX® MBTSfrom Chemtura USA Corporation (Middlebury, Conn.) and ALTAX® from R.T.Vanderbilt Company, Inc., dipentamethylenethiuram hexasulfide, such asSULFADS® from R.T. Vanderbilt Company, Inc., butyl zimates, such as zincdi-n-butyldithiol carbamate and phosphates, such as RHENOCURE®, which iscommercially available from Rhein-Chemie Reinau GMBH (Mannheim, Germany)and ACCELERATOR VS from Akrochem Chemical Corp., and combinationsthereof. The cure accelerator may be included in the precursor of theinsulative composition in an amount of between about 0.1 wt % and about1 wt % of the total weight of the precursor of the insulativecomposition and, more particularly, between about 0.25 wt % and about0.8 wt % of the total weight of the precursor of the insulativecomposition. In some embodiments, the cure package may include laccofinesulfur as the sulfur-based curing agent and NAUGEX® MBTS and TMTD ascure accelerators. For example, the precursor of the insulativecomposition may include about 1.31 wt % laccofine sulfur, about 0.65 wt% NAUGEX® MBTS and about 0.33 wt % TMTD.

The insulative composition may also, optionally, include at least oneadditive to achieve the desired properties in the insulativecomposition. As a non-limiting example, additives that may be used inthe insulative composition may include an antioxidant, a tackifier, aprocessing aid, a plasticizer and an activator.

At least one antioxidant may be included in the precursor of theinsulative composition to stabilize the NBR. For example, the precursorof the insulative composition may include an amine antioxidant, such asAGERITE® STALITE®, AGERITE® resin, AGERITE SUPERFLEX®, and combinationsthereof. AGERITE® STALITE®, AGERITE® resin and AGERITE® SUPERFLEX® arecommercially available from R.T. Vanderbilt Company, Inc. (Norwalk,Conn.). AGERITE® STALITE® may include a mixture of alkylateddiphenylamines, such as a mixture of benzenamine, N-phenyl-, reactionproducts with styrene and 2,4,4-trimethylpentene, and diphenylamine.AGERITE® SUPERFLEX® may include diphenylamine-acetone reaction products,calcium silicate and diphenylamine. AGERITE® resin may includebenzenamine, and N-phenyl-, reaction products with2,4,4-trimethylpentene. The antioxidant may be included in the precursorof the insulative composition in an amount of between about 1 wt % andabout 3.5 wt % of the total weight of the precursor of the insulativecomposition and, more particularly, between about 1.5 wt % and about 2.5wt % of the total weight of the precursor of the insulative composition.

Tackifiers may include materials that develop a high tack level in theNBR, such as phenolic resins, polybutenes, hydrocarbons, andcombinations thereof. For example, the tackifier may be a phenolicresin, such as AKROCHEM® P-133, AKROCHEM® P-104, AKROCHEM® P-172,AKROCHEM® P-183 and AKROCHEM® P-90, each of which is commerciallyavailable from Akrochem Corporation (Akron, Ohio), a hydrocarbon resin,such as WINGTACK® 95, which is commercially available from Cray Valley(Houston, Tex.), DUREZ® 31671, which is commercially available fromDurez Corporation (Addison, Tex.) and DYPHENE® 8318 or DYPHENE® 8320which are commercially available from Western Reserve Chemical (Stow,Ohio). AKROCHEM® P-133 is a thermoplastic, alkyl phenolic resin in afree-flowing flake form having a specific gravity of about 1.04, amelting point of about 97° C. and a Gardner-Holdt viscosity of about 0.The tackifier may be included in the precursor of the insulativecomposition in an amount of between about 4 wt % and about 12 wt % ofthe total weight of the precursor of the insulative composition and,more particularly, between about 6 wt % and about 10 wt % of the totalweight of the precursor of the insulative composition.

By way of non-limiting example, processing aids may include a stearicacid, such as INDUSTRENE® B, which is commercially available fromCrompton Corporation (Greenwich, Conn.), dicarboxylic and tricarboxylicester-based compounds, naphthenic processing oils, and combinationsthereof. The processing aid may be included in the precursor of theinsulative composition in an amount of between about 0.1 wt % and about2 wt % of the total weight of the precursor of the insulativecomposition and, more particularly, between about 0.5 wt % and about 1.5wt % of the total weight of the precursor of the insualtive composition.

The insulative compound may additionally include a plasticizer, such asa dioctyl phthalate (DOP), a dioctyl adipate (DOA), a dioctylterephthalate (DOTP), and combinations thereof. The plasticizer may beincluded in the precursor of the insulative composition in an amount ofbetween about 4 wt % and about 12 wt % of the total weight of theprecursor of the insulative composition and, more particularly, betweenabout 6 wt % and about 10 wt % of the total weight of the precursor ofthe insulative composition.

Activators include, for example, metal oxides, such as zinc oxide (e.g.,KADOX® 720 C, which is commercially available from Horsehead Corp.(Monaca, Pa.)) and magnesium oxide (e.g., ELASTOMAG® 170, from MortonChemical Co. (Chicago, Ill.)). The cure activator may be included in theprecursor of the insulative composition in an amount of between about 1wt % and about 5 wt % of the total weight of the precursor of theinsulative composition and, more particularly, between about 2 wt % andabout 3.5 wt % of the total weight of the precursor of the insulativecomposition.

Relative amounts of the NBR, the nanoclay, the cure package and theadditives, if present, in the precursor of the insulative compositionmay be adjusted to achieve desired rheological, physical and mechanicalproperties, such as a desired specific gravity, compressive modulus,pre-cure viscosity, scorch properties, density, cure time, Shore Ahardness, tensile strength or elongation at failure. The insulativecomposition of the present disclosure may have a substantially reducedspecific gravity and compressive modulus in comparison to conventionalNBR and SFNBR compositions and, thus, a thickness of the insulativecomposition of the present invention may be substantially reduced inballistic applications. In addition, prior to curing, the precursor ofthe insulative composition may have a flowable consistency and anincreased cure rate that provide improved fabrication efficiency.

The precursor of the insulative composition may be prepared by mixingthe nanoclay with the NBR and one or more of the optional ingredients,if present, to form a master batch. During mixing, the master batch mayreach a maximum temperature of between about 143° C. and about 154° C.and, more particularly about 148.89° C. (about 300° F.). The masterbatch may be mixed until the nanoclay and any optional ingredients aresubstantially evenly distributed in the NBR matrix. For instance, themaster batch may be mixed for between about 5 minutes and about 25minutes and, more particularly, about 12 minutes to promote exfoliationof the nanoclay by the NBR. Any remaining optional ingredients, ifpresent, may be added and mixed into the master batch. The temperatureof the master batch may be lowered before adding the cure package toprevent premature curing of the precursor insulative composition. Forinstance, during the curative mixing, the master batch may be exposed toa maximum temperature of between about 78° C. and about 100° C. and,more particularly about 87.78° C. (about 190° F.) before adding the curepackage. About one-half (½) of a total volume of the master batch mayinitially be added to the cure package and mixed and, thereafter, thebalance of the master batch (i.e., the remaining one-half (½) of thetotal volume of the master batch) may be mixed to form a precursorcomposition. The master batch and the cure package may be mixed untilthe precursor composition has a desired, flowable consistency. Theinsulative composition may be prepared in conventional rubber mixingequipment, such as in an internal mixer, a sigma blade mixer, a verticalblade mixer, or a compounding extruder mixer. Rubber mixing equipment isknown in the art and, therefore, is not described in detail herein. Theprecursor composition may cure within between about one (1) minute andabout ten (10) minutes to form the insulative composition. The precursorcomposition may be stored in the flowable state at temperature of about0° C. less than or equal to about one (1) year. The ability of theprecursor to be easily molded and quickly cured enables increasedproduction rates of articles including the insulative composition.

By forming the master batch including the NBR and the nanoclay andoptional ingredients, if present, prior to adding the ingredients of thecure package, exfoliation and distribution of the nanoclay throughoutthe NBR is provided. Furthermore, mixing the nanoclay with the NBR andwith fillers, such as the antioxidant and the processing aid, ifpresent, before mixing with the other ingredients results in improvedexfoliation and distribution of the nanoclay throughout the NBR.

The precursor of the insulative composition may be placed into a mold toform a desired shape, such as a sheet, and cured for use in an article,such as personnel body minor, ground vehicle armor and aircraft armorsystems. In some embodiments, the sheet of the insulative compositionmay be used in a layered article including alternating layers of theinsulative composition and a support material. For example, the supportmaterial may be a metal, plastic, a mesh or a fibrous material, such asDYNEEMA®, SPECTRA®, TECHNORA®, VECTRAN®, polyester, nylon or propylene.FIG. 1 illustrates an example of an article 10 including layers of theinsulative composition 12 disposed between layers of a support material14. In the embodiment shown in FIG. 1, the insulative composition 12 isdisposed between sheets of the support material 14 to form the article10 that includes a plurality of layers. In other embodiments (notshown), a single layer of the insulative composition 12 may be disposedon the support material 14 as a reinforcement or barrier layer. Thearticle 10 may be formed by -curing the precursor of the insulativecomposition (not shown) into a mold or directly onto the supportmaterial 14 to form a sheet of the insulative composition 12. Since thelow compressive modulus and low specific gravity of the insulativecomposition results in reduced weight, improved strength and improvedshock absorption, a thickness of the insulative composition may bereduced while providing improved ballistic performance.

The following examples serve to explain embodiments of the presentinvention in more detail. These examples are not to be construed asbeing exhaustive or exclusive as to the scope of this invention.

EXAMPLES Example 1 Formulation of Insulative Composition

A precursor of an insulative composition (“Precursor Composition”)having the ingredients shown in Table 2 was formulated. The NIPOL® 1052was mixed for about 1 minute. The CLOISITE® 10 A, the AGERITE® STALITE®,and the INDUSTRENE® B were then added to the NIPOL® 1052 and mixed forabout 12 minutes to form a mixture. The remaining ingredients (i.e., theAKROCHEM® P-133 resin, the KADOX® 720 C and the dioctyl phthalate),except for the cure package, were then added to the mixture to form amaster batch. The dioctyl phthalate was added slowly to the reactionmixture to prevent coagulation. During mixing, the temperature of themaster batch was maintained at less than or equal to about 148.89° C.(300° F.). The ingredients of the master batch were mixed until theingredients were substantially homogeneously dispersed in the NIPOL®1052. The temperature of the master batch was reduced to a temperatureof between about 21.11° C. (70° F.) and about 37.38° C. (100° F.) beforeabout one-half (½) of the total volume of the master batch was added tothe ingredients of the cure package (i.e., the laccofine sulfur, theNAUGEX® MBTS and the tetramethyl thiuram disulfide. The ingredients weremixed until they were substantially evenly distributed and then abalance of the master batch (i.e., the remaining one-half (½) of thetotal volume of the master batch) was added and mixed. The viscosityresulting precursor composition was sufficiently high to enable moldingof the precursor composition into desired shape.

TABLE 2 Precursor Composition Material Parts wt % NIPOL ® 1052 (NBR) 10062.25 CLOISITE ® 10A (nanoclay) 15 9.79 AGERITE ® STALITE ® (amineantioxidant) 3 1.96 AKROCHEM ® P-133 RESIN (phenolic resin) 12.75 8.32INDUSTRENE ® B (stearic acid) 1.5 0.98 Dioctyl Phthalate (DOP) 12.5 8.16KADOX ® 720C (zinc oxide) 5 3.26 laccofine sulfur 2 1.31 NAUGEX ® MBTS(benzothiazyl disulfide) 1 0.65 tetramethyl thiuram disulfide (TMTD) 0.50.33

Example 2 Rheological Properties of the Precursor Composition

The rheological properties of the Precursor Composition described inExample 1 were determined by conventional techniques. The results of therheological testing are shown in Table 3. For comparative purposes, therheological properties of a precursor of a conventional SFNBRcomposition, which is available from Kirkhill Elastomers (Brea, Calif.),are also provided. Mooney viscosity and Mooney Scorch of the precursorcompositions were measured at 100° C., respectively, with a Mooney MV2000 of Alpha Technologies (USA). Other rheological properties weredetermined using Oscillating Disc Rheometer ODR-100 S of AlphaTechnologies (USA). For comparative purposes, available mechanical andphysical properties of the conventional SFNBR composition are alsoshown.

TABLE 3 Rheological Properties of the Precursor Composition and SFNBRComposition A SFNBR Mooney Viscosity at about 100° C. 24.4 Mooney Scorchat about 121.1° C. 13.6 Minimum torque (ML)  4.16 >11 Maximum torque(MH) 57.04 >86 Scorch time (TS2)  2.92 min  >5 min Optimum vulcanizationtime  4.29 min >12 min (T90)

A comparison of the rheological properties of Composition A and theconventional SFNBR composition was made. The comparison showed thatComposition A exhibited a substantially reduced minimum torque, maximumtorque, scorch time, and optimum vulcanization time in comparison to theconventional SFNBR composition. The comparison showed that Composition Ahad superior rheological properties in comparison to the conventionalSFNBR rubber.

The Precursor Composition exhibited a viscosity of about 24.4 and had aflowable consistency about twenty four (24) hours after mixing. Theviscosity of the Precursor Composition may be maintained by storing thePrecursor Composition at a temperature of less than or equal to about 0°C. (32° F.).

Example 3 Mechanical and Physical Properties of the InsulativeComposition

The Precursor Composition described in Example 1 was cured to form aninsulative composition (“Composition A”) and the mechanical and physicalproperties were determined. Table 4 shows the mechanical and physicalproperties of Composition A. These properties were determined byconventional techniques. For comparative purposes, the mechanical andphysical properties of the SFNBR composition are also shown.

TABLE 4 Comparison of Mechanical and Physical Properties of CompositionA and a SFNBR Composition Composition A SFNBR Specific gravity 1.071.18-1.26 Tensile strength 900 >1750 Elongation at failure 419 >400Shore A Hardness 57 60-80 Compressive modulus 507 psi 1210 psi

Composition A was tested for physical properties (specific gravity) andmechanical properties (tensile strength, elongation at failure, shore Ahardness and compressive modulus). A comparison of the physicalproperties and mechanical properties of Composition A and theconventional SFNBR composition was made. The comparison showed thatComposition A had a substantially reduced specific gravity and, thus,exhibited a weight of about 14% less than the conventional SFNBRcomposition. The comparison showed that Composition A had superiorstrength and compressive modulus in comparison to the conventional SFNBRrubber.

The invention has been described herein in language more or lessspecific as to composition structural and methodical features. It is tobe understood, however, that the invention is not limited to thespecific features shown and described, since the means herein disclosedcomprise preferred forms of putting the invention into effect. Theinvention is, therefore, claimed in any of its forms or modificationswithin the proper scope of the appended claims appropriately interpretedin accordance with the doctrine of equivalents.

1. An insulative composition, comprising, before curing: at least onenitrile butadiene rubber comprising between about 60% by weight andabout 70% by weight of a total weight of the insulative composition; ananoclay; and a cure package comprising a sulfur-based curing agent. 2.The insulative composition of claim 1, wherein the at least one nitrilebutadiene rubber comprises about 62.25% by weight of a total weight ofthe insulative composition.
 3. The insulative composition of claim 1,wherein the nanoclay comprises a montmorillonite clay.
 4. The insulativecomposition of claim 1, wherein the cure package further comprises atleast one of tetramethyl thiuram disulfide and benzothiazyl disulfide.5. The insulative composition of claim 4, wherein the sulfur-basedcuring agent comprises about 1.31% by weight of the total weight of theinsulative composition, the tetramethyl thiuram disulfide comprisesabout 0.33% by weight of the total weight of the insulative composition,and the benzothiazyl disulfide comprises about 0.65% by weight of thetotal weight of the insulative composition.
 6. The insulativecomposition of claim 1, wherein the nanoclay comprises between about 8%by weight and about 12% by weight of the total weight of the insulativecomposition.
 7. The insulative composition of claim 1, furthercomprising at least one of an antioxidant, a tackifier, a processingaid, a plasticizer, and an activator.
 8. The insulative composition ofclaim 1, further comprising at least one of an amine antioxidant, aphenolic resin, stearic acid, dioctyl phthalate, and zinc oxide.
 9. Aninsulative composition, comprising, before curing: a polymer comprisingat least one nitrile butadiene rubber; a nanoclay; and a cure packagecomprising a sulfur-based curing agent and at least one of tetramethylthiuram disulfide and benzothiazyl disulfide, wherein the insulativecomposition is an isotropic material.
 10. The insulative composition ofclaim 9, wherein the cure package consists of the sulfur-based curingagent, the tetramethyl thiuram disulfide, and the benzothiazyldisulfide.
 11. The insulative composition of claim 10, wherein thesulfur-based curing agent consists of about 1.31% by weight of a totalweight of the insulative composition, the tetramethyl thiuram disulfidecomprises about 0.33% by weight of the total weight of the insulativecomposition, and the benzothiazyl disulfide comprises about 0.65% byweight of the total weight of the insulative composition.
 12. Theinsulative composition of claim 9, wherein the at least one nitrilebutadiene rubber comprises from about 26% by weight to about 35% byweight of a total weight of the insulative composition.
 13. Theinsulative composition of claim 9, wherein the nanoclay is homogeneouslydispersed within the polymer.
 14. The insulative composition of claim 9,wherein the nanoclay comprises magnesium aluminum silicate plateletsmodified with a quaternary ammonium salt.
 15. The insulative compositionof claim 9, further comprising at least one of an amine antioxidant, aphenolic resin, stearic acid, dioctyl phthalate, and zinc oxide.
 16. Aprecursor composition comprising: a polymer comprising at least onenitrile butadiene rubber; a nanoclay; and a cure package comprising asulfur-based curing agent, wherein the precursor composition has aflowable consistency.
 17. The precursor composition of claim 16, whereinthe precursor composition has a Mooney viscosity of between about 5 andabout
 30. 18. An article of manufacture, comprising: a sheet of fibrousmaterial; and a precursor composition disposed on the sheet of fibrousmaterial, comprising: at least one nitrile butadiene rubber; a nanoclay;and a cure package comprising a sulfur-based curing agent and at leastone of tetramethyl thiuram disulfide and benzothiazyl disulfide, whereinthe precursor composition is fiber-free.
 19. A method of forming aprecursor of an insulative composition, comprising: exfoliating ananoclay with a polymer comprising at least one nitrile butadiene rubberto form a master batch comprising a homogeneous mixture of the nanoclayand the polymer; mixing a portion of the master batch with a cure agentto form a mixture; and combining a remaining portion of the master batchwith the mixture to form a precursor composition having a flowableconsistency.
 20. The method of claim 19, wherein exfoliating a nanoclaywith a polymer comprising at least one nitrile butadiene rubber to forma master batch comprising a homogeneous mixture of the nanoclay and thepolymer comprises mixing the at least one nitrile butadiene rubber withthe nanoclay for between about 5 minutes and about 25 minutes to formthe master batch.
 21. The method of claim 19, wherein exfoliating ananoclay with a polymer comprising at least one nitrile butadiene rubberto form a master batch comprising a homogeneous mixture of the nanoclayand the polymer further comprises mixing an amine antioxidant and aphenolic resin with the master batch.
 22. The method of claim 19,wherein mixing a portion of the master batch with a cure agent to form amixture comprises mixing about one-half of a total volume of the masterbatch with the cure agent to form the mixture.
 23. The method of claim19, wherein mixing a portion of the master batch with a cure agent toform a mixture comprises mixing the master batch with laccofine sulfurand at least one of tetramethyl thiuram disulfide and benzothiazyldisulfide to form the mixture.
 24. The method of claim 19, furthercomprising adding at least one of a tackifier, an activator and aplasticizer to the master batch before mixing the portion of the masterbatch with the cure agent.
 25. The method of claim 19, wherein combininga remaining portion of the master batch with the mixture to form aprecursor composition having a flowable consistency comprises combiningthe remaining portion of the master batch with the mixture to form aprecursor having a Mooney viscosity of less than about
 30. 26. Theinsulative composition of claim 1, wherein the insulative composition isan isotropic material.